A table for defining the position of a sheet-metal piece in a system for producing bent sheet-metal articles

Abstract: A table for defining the position of a piece to be bent by means of an automatic system including a bending machine and a manipulator which can grip a piece to be bent comprises means (134) for defining a position for the location of the piece relative to the table (96) and means (146) for fitting a gripper (98) on to the piece in a predetermined position.

Description: Technical field The present invention relates to the production of bent sheet-metal articles and concerns a table for defining the position of a sheet-metal piece to be bent by means of an automatic system including a bending machine and a manipulator. Background Art The invention has been developed to solve the problem of the bending of sheet-metal articles of complex shapes which are frequently used in machines such as photocopiers, facsimile machines and various electronic devices. These products are subject to rapid development and manufacturers therefore often change models from one year to another. Each new model is the product of a redesign, even as regards the various sheet-metal articles which it contains. These bent sheet-metal articles are therefore produced on a relatively small scale and thus do not justify complex and expensive tools and dies. A system for producing bent sheet-metal articles known from document US-A-4 991 422 departs radically from previously existing bending systems which use bending presses with fixed frameworks and linear, V-sectioned punches and dies which are movable vertically towards and away from each other. The system described in US-A-4 991 422 provides for a piece which is to be bent to be supported by a manipulator so that a region of the piece which is to be bent lies in a vertical suspension plane. The bends are effected by means of an oscillating bending machine having two tools which can be disposed in any configuration relative to the piece to be bent. The piece is supported by the manipulator in a manner such that it can perform movements of limited extent with five degrees of freedom, excluding rotation about an axis perpendicular to the plane of the undeformed piece of sheet metal. Disclosure of the Invention The object of the present invention is to develop a table for defining the position of a sheet-metal piece to be bent by means of a bending system the essential elements of which are described in the aforementioned US-A-4 991 422. The object of the invention is achieved by means of a table having the characteristics defined in the claims. Brief Description of the Drawings The present invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic, perspective view showing a system embodying the invention, Figures 2 to 11 show a table according to a preferred embodiment of the invention for defining the position of a piece to be bent and, more precisely, Figures 2 to 4 show in section, in elevation, and in plan, a gripper for fitting on to a piece of sheet metal, Figure 5 is a plan view of the table indicated by the arrow V in Fig. 1, Figure 6 is a schematic section taken on the line VI-VI of Figure 5, Figure 7 is a longitudinal section of the part indicated by the arrow VII in Figure 5, Figure 8 is a section of the part indicated by the arrow VIII in Figure 7, on an enlarged scale, and Figures 9, 10 and 11 are schematic views showing the part indicated by the arrow IX in Figure 5, on an enlarged scale, Best Mode for Carrying out the Invention A system for producing bent sheet-metal articles and a table being part of the system will now be described with reference to the drawings. The system for producing sheet-metal articles With reference to Figure 1, a system for producing bent sheet-metal articles from blanked or laser-cut pieces of sheet metal of shapes corresponding to the development in a plane of the articles to be produced, is generally indicated 50. The system 50 comprises a station 52 for positioning the pieces of sheet metal, a measurement and storage station 54, a bending station 56, an output station 58 and a device 60 for the automatic replacement of the tools, with a respective tool store 62. The bending station 56 comprises a cartesian manipulator 64 including a vertically-movable device 66 carried by a carriage 68 movable along a beam 70 which in turn is movable along guides 72 of a portal structure 74. The movable device 66 of the manipulator 64 carries a suspension head 76 which will be described in detail below, for holding vertically, by means of a gripper, a piece of sheet-metal to be bent. The suspension head 76 of the manipulator 64 supports the piece in a manner such that it floats freely, so that the piece is free to perform movements of a limited extent during bending. In order to execute each bend, the manipulator 64, which is controlled by a conventional control unit 78, positions the piece in a position which is determined on the basis of a program established in dependence on the geometrical shape of the piece to be worked. The bending station 56 also comprises a bending machine 80 comprising a tool-holder structure 82 having a punch 84 and a die 86 which cooperate with each other. The tool-holder structure 82 is rotatable about an axis which passes through the bending line defined by the vertex of the V-shaped punch 84 and can also pivot about a horizontal axis perpendicular to the aforesaid axis of rotation. It will therefore be appreciated that the punch 84 and the die 86 can be disposed in any position relative to the piece to be bent. The rotary and pivoting movements of the tool-holder structure 82 are brought about by the control unit 78 on the basis of a predetermined program. It is important to underline that the precision of the positioning of the piece in space, like the precision of the positioning of the tools, is of decisive importance since, unlike conventional bending methods, there are neither mechanical abutments to define the position of the piece nor systems for measuring the position of the piece relative to the bending machine. The necessary precision in the positioning of the piece is achieved by virtue of a preliminary determination of the relative piece-manipulator position and of the precise control of the relative manipulator-bending machine positions, which is achieved by virtue of the operating precision of the manipulator 64 and of the bending machine 80. The operating principle upon which the bending system of Figure 1 is based thus consists of the positioning of a piece of sheet metal in a predetermined region in space with great precision and repeatability, and of the modification of the positions of the bending tools relative to the piece, with a corresponding degree of precision and repeatability, by a movement of the bending machine, so as to execute the bend in the desired region. For further clarification as regards the operating principle of the system according to the present invention, reference should be made to US-A-4 991 422. The main characteristic of the system according to Figure 1 is its ability to work on extremely small batches (even a single piece) of pieces with different geometrical shapes, solely by means of the selection of a different working program, without carrying out tooling operations. A problem which had to be solved in order to achieve a high degree of flexibility of the system was that of devising a unit for loading the pieces which enabled shaped pieces of sheet metal of complex shapes and extremely variable dimensions to be stored and subsequently gripped by the suspension head 76 of the manipulator 64. With conventional grippers carried by the head of the manipulator, in addition to the difficulty of producing a universal gripper which can grip pieces of different geometrical shapes, there is the problem of the precise positioning of the piece relative to the gripper and hence relative to the locating system of the manipulator, that is, the problem of how to position the piece precisely on a loading device which, at the same time, can be adapted to pieces which differ greatly in shape and size. In the system according to Figure 1, these problems have been overcome by virtue of the fact each piece is associated with its own gripper which is fitted on to a predetermined region of the undeformed piece of sheet metal. The gripper is fitted on to the piece of sheet metal in the positioning station 52 in the manner which will be described in detail below. The pieces, with their respective grippers, are disposed in a store 90 to await transfer to the bending station 56. The store 90 can easily house pieces of different geometrical shapes without the need for any tooling, by virtue of the use of the gripper. In fact, the store 90 can accommodate a certain number of grippers which are inserted in a corresponding number of forks forming part of the store. The pieces of sheet metal, each gripped by its own gripper, are disposed vertically, suspended by the gripper itself, and thus have no direct connection with the store 90 which is completely independent of the shapes of the sheets. After each piece of sheet metal has been provided with its gripper, the piece is subjected to a measurement step carried out by means of a conventional feeler 88. The data detected by this measurement are processed and stored by the control unit 78 which establishes the link which exists between a locating system fixed relative to the piece and a locating system which is fixed relative to the gripper and, consequently, is fixed relative to the suspension head 76 of the manipulator 64. Small corrections can thus be made to the program controlling the manipulator 64 to compensate for errors in the positioning of the piece relative to the gripper. The piece may be measured when it is already connected to the suspension head 76 of the manipulator 64. In this case, the feeler 88 must be movable in order to enter and leave the working area. If the cycle for the working of the piece provides for the gripping region to be changed after some bends have been effected, a new measurement can be made after the piece has been gripped in the new position. Alternatively, and as shown in Figure 1, the measurement may be effected outside the working area, without affecting the time taken by the bending cycle, whilst the piece is supported by an auxiliary manipulator 89. An alternative could be that of ensuring sufficient precision in the positioning of the piece relative to the gripper at the moment when the gripper is fitted on to the piece so as to avoid the measurement step altogether. Upon completion of the bending operations, the manipulator 64 brings the worked article to an output station 58, shown schematically by means of a belt conveyor. There may be a device 92 in the output station 58 for removing the grippers from the sheet-metal articles. The table for defining the position of a piece to be bent As has been seen above, each piece to be bent is fitted with its own gripper. This step is carried out on a table, indicated 96 in Figure 1, for defining the position of a piece. Before the structure and operation of the positioning table 96 are described, the gripper, which is shown in Figures 2, 3, and 4 and indicated 98, will be described. The gripper 98 is a purely passive element, that is, it does not have opening and closure mechanisms of its own. The gripper 98 is constituted by a monolithic metal body having two resilient arms 100, to the ends of which two plates of frictional material 102, between which a piece of sheet metal can be gripped, are fixed. A cavity 104 (Figure 2) is defined between the two arms 100 for housing a mechanism for moving the arms 100 apart resiliently. The gripper 98 has a shank 106 with a tapered outer surface for engagement on the suspension head of the manipulator. The shank 106 has a through-hole 108 which communicates with the cavity 104 and has a seat 110 for engagement by means which connect the gripper 98 to the manipulator head. The gripper 98 also has a pin 112 for the angular location of the gripper relative to the manipulator head and a groove 114 for engagement by a retaining device when the gripper is fitted on a piece of sheet metal. Although the gripper just described is advantageous because of its structural simplicity, grippers of other types, even with mechanical closure, could be used. An alternative type of gripper could be constituted by one fixed arm and one movable arm which could be tightened against the fixed arm by means of a screw operated by an external device independent of the gripper. As explained above, the gripper 98 has to be fitted on to the piece of sheet metal to be bent in a predetermined position. According to the present invention, this is achieved by virtue of a positioning table 96 which has a device for holding a gripper 98 in a predetermined region of the table 96. The table 96 also has means for defining a position for the location of the piece of sheet-metal relative to the table 96. Figures 5 and 6 show a preferred embodiment of the table 96 in which the locating means are in the form of abutment elements projecting from the surface which supports the piece. Any mechanical or optical system which can define a position for the location of the piece is intended, however, to fall within the scope of the present invention. With reference to Figure 5 and 6, a fixed support structure of the table 96 is indicated 114. The structure 114 has an upper rectangular frame on two sides of which there are parallel guides 116 between which the ends of a plurality of elongate elements 118 are engaged for sliding freely, the elements 118 defining a support plane for a piece of sheet metal to be positioned. The elongate elements 118 can slide freely independently of each other in the directions indicated by the double arrow 120. As can be seen in greater detail in Figure 6, a pair of guides 122 is disposed transversely beneath the elongate elements 118 and two cross-members 124, parallel to the elongate elements 118 and having their own conventional movement means (not shown), are slidable thereon. The two cross-members 124 have respective guides 126 which are parallel to the elements 118 and along each of which a carriage 128 having its own movement system, is slidable. Again with reference to Figure 6, each cross-member 124 has a pair of vertically-movable pins 130 which can engage respective seats 132 in the lower portions of the elongate elements 118. Each carriage 128 has an abutment element 134 which can travel vertically relative to the carriage. As can be seen in the left-hand portion of Figure 6, each abutment element 134 is intended to project above the support surface of the table 96 through a slot 136 formed by the separation of two sets of elongate elements 118. The support structure 114 of the table 96 carries four thrust actuators 138 which act on the elongate elements 118 and compact them against a central fixed cross-member 140. A position for the location of a piece of sheet metal on the support surface of the positioning table 96 is created as follows. The abutment elements 134 are brought to their lowered configuration (see the right-hand portion of figure 6) in which they do not interfere with the elongate elements 118. The four actuators 138 are then operated and compact the slidable elements 118 towards the centre of the table. The pins 130 of the cross-members 124 are then brought into correspondence with the longitudinal element 118 situated in the region of the table 96 in which the slot 136 for the passage of the abutment element 134 is to be created. When the cross-members 124 are in the correct positions, the pins 130 are raised so as to engage the seats 132 in the element 118. The actuators 138 are then brought to their retracted, inoperative positions and the cross-members 124 are moved outwardly relative to the table, creating the slot 136 through which the abutment element 134 can extend. After the slot 136 has been created, the carriage 128 of each cross-member 124 is moved along the slot until it reaches a predetermined point on the support surface. When a piece of sheet-metal is disposed, manually or by means of an automatic manipulator, on the support surface of the table 96, the position of the piece of sheet-metal relative to the table is thus determined univocally by the two abutment elements 134. If the pieces are positioned on the table manually, there will be a display unit (not shown) in the vicinity of the table 96 to show the operator the correct orientation of the piece. In order to improve the precision of the positioning of the piece of sheet-metal, each abutment element 134 has four parallel pins 142, as shown schematically in Figures 9, 10 and 11. The four pins 142 are perpendicular to the surface supporting the piece and are rotatable together, with a stepped movement, about an axis 144 perpendicular to the plane of Figures 9 to 11. Each abutment element 134 can thus serve for the positioning of a corner of the piece of sheet-metal (Figure 9), of an angle (Figure 10), or of a flat edge (Figure 11). Naturally, the number of pins 142 could be other than four, since the same function can be achieved by any number of pins greater than two. As an alternative to the system described above for positioning the pieces with the use of mechanical abutments, an optical system consisting of the projection of a shadow or an image of a shape corresponding to that of the piece to be positioned onto the support surface could be used. For large batches, the table 96 may be replaced by a jig which can be fitted out, for example, with fixed pins arranged manually. A device for fitting a gripper 98 on to a piece of sheet-metal positioned in the manner described above, is schematically indicated 146 in Figures 5 and 6. As can seen in greater detail in Figure 7, the device 146 comprises a tubular element 148, fixed to the structure 114 of the table 96, for holding a gripper 98. The rocker arm 152 is kept in the engagement position by a spring 153 and is associated with a release actuator 154. The device 146 comprises a device 156 for moving the resilient arms 100 of the gripper 98 apart. The device 156 comprises a pair of spreader arms 158 formed with protrusions 158a and carried by a body 160 which is movable in the directions indicated by the double arrow 162 and is operated by an actuator 164. A rod 166 formed with tapered sections 166a extends between the two spreader arms 158 and can perform an axial movement of limited length relative to the arms. As will be described in detail below, the tapered sections 166a are engageable with the protrusions 158a. The rod 166 is connected to a second actuator 165 carried by the body 160. The operation of the first actuator 164 inserts the rod 166 and the spreader arms 158 in the cavity 104 of the gripper 98 until they reach the position shown in Figure 7. The operation of the second actuator 165 then slides the rod 166 relative to the spreader arms 158 as shown in Figure 8 so as to move the arms 158 apart and open out the resilient arms 100 of the gripper 98. The gripper is closed again under the effect of the resilient return of the arm 100 by the retraction of the rod 166 by the means of the second actuator 165. It could be noted that, by virtue of the system for moving the arms 158 apart by means of the slidable rod 166, no axial force is exerted on the gripper, which would be undesirable, but only spreading forces are exerted thereon. After the gripper 98 has been fitted on a piece of sheet metal, the gripper is released by the retraction of the spreader arms 158 and the rod 166 by means of the actuator 164 and, finally, the locking of the rocker arm 152 by means of the actuator 154.

Claims: A table for defining the position of a piece to be bent by means of an automatic system including a bending machine (80) and a manipulator (64) which can grip a piece to be bent comprising means (134) for defining a position for the location of the piece relative to the table (96) and means (146) for fitting a gripper (98) on to the piece in a predetermined position. A table according to Claim 1, characterized in that the means for defining a position for the location of the piece comprise at least one pair of abutment elements (134) which project from a surface for supporting the piece and the positions of which can be varied relative to the support plane in dependence on the geometrical shape of the piece. A table according to Claim 2, characterized in that the surface for supporting the piece is constituted by a plurality of elongate elements (118) which can slide independently of each other in guides (116) disposed transverse the elongate elements (118). A table according to Claim 3, characterized in that it comprises a movement device (130) disposed beneath the support plane for moving the elongate elements (118) so as to create at least two slots (136) which are parallel to the axes of the elongate elements (118) and through which the abutment elements (134) can move. A table according to Claim 4, characterized in that the movement device comprises a pair of cross-members (124) which are slidable transverse the elongate elements (118) and have means (130) for engaging respective elongate elements (118). A table according to Claim 5, characterized in that each cross-member (124) of the movement device carries a carriage (128) movable transverse the direction of sliding of the cross-members (124) and having a respective abutment element (134). A table according to any one of Claims 2 to 6, characterized in that each abutment element (134) comprises a base which can move perpendicular to the support plane and carries at least two pins (142) parallel to each other and perpendicular to the support plane and defining a support for the edge of the piece of sheet metal to be positioned. A table according to Claim 7, characterized in that each abutment element (134) can perform an adjustment movement about an axis (144) perpendicular to the support plane. A table according to Claim 1, characterized in that it comprises a device (146) for holding a gripper (98) in a predetermined position relative to the table, the gripper (98) comprising a pair of resilient arms (100) between which a piece of sheet metal can be gripped, the gripper-holding device (146) comprising a device (156) for keeping the resilient arms (100) of the gripper (98) in a spread-out position in order to fit the gripper (98) on a respective piece of sheet metal. A table according to Claim 9, characterized in that the device (156) for keeping the arms of the gripper (98) in the spread-out position comprises a pair of spreader arms (158) carried by a movable body (160) which inserts the spreader arms (158) between the resilient arms (100) of the gripper (98), the spreader arms (158) being associated with a slidable rod (166) operated by an actuator (165) carried by the movable body (160). A table according to Claim 8, characterized in that it comprises actuators (138) acting on the elongate elements (118), for compacting them against a 'central fixed cross-member (140). A table according to Claim 10, characterized in that the spreader arms (158) are formed with respective protrusions (158a) at their free ends, and the slidable rod (166) is formed at its free end with tapered sections (116) for engaging the protrusions (158a). A table according to Claim 10, characterized in that it comprises a rocker arm (152) for engaging a groove formed in the gripper (98). A table according to any of the preceding Claims, characterized by a feeler (88) for measuring the piece, which is connected to an auxiliary manipulator (89).

Inventors: SARTORIO FRANCO, SARTORIO, FRANCO
Applicants: AMADA CO LTD, CREA SRL, AMADA COMPANY, LTD., CREA S.R.L.
Application year: 1994
Main classification: B21D11
IPC codes: B21D5, B21D11, B21D37, B21D43